SPIN DELOCALIZATION IN DIPYRIDINE ADDUCTS OF SOME HETEROATOM-SUBSTITUTED BIS(ACETYLACETONATE)NICKEL(2) COMPLEXES

The proton magnetic resonance spectra of the paramagnetic, dipyridine adducts of bis acetylacetonates, β-ketoimines, and monothioacetylacetonates of nickel(II) are reported. The contact shifts for the bidentate ligands are a sensitive function of the variable coordinating heteroatom, with the extent of a delocalization increasing as N < O < S, while the T delocalization apparently decreases as N > O > S. The relative extents of α spin delocalization are consistent with the expected ordering of the ligand field strengths of the heteroatoms in the order β-keto imine > acetylacetone > monothioacetylacetone. The dependence of the bis(β-keto imine)nickel(II) complex contact shifts on pyridine concentration indicates that the presence of pyridine shifts the tetrahedral square-planar equilibrium to the right from that observed in chloroform. © 1969, American Chemical Society. All rights reserved.